A single gustatory fiber in the chorda tympani nerve of the rat responds to the stimulation of more than one single taste bud. Individual chemical stimulation of one of the taste buds innervated by a single fiber results in a reproducible response to a given concentration of chemical stimulus. Stimultaneous stimulation of the taste buds surrounding the isolated one results in enhancement or depression of the isolated taste bud response, depending on the kind and concentration of chemical stimulus used. With sodium chloride used to stimulate the isolated papilla, application of potassium benzoate to the surrounding papilla produces a depression; application of sodium chloride to the surrounding papillae produces enhancement. The interactions among separate inputs to a single primary nerve provide a model for the study of the ionic mechanisms of excitatory and inhibitory gustatory receptor processes against a background of a controlled response. The proposition that the cation is excitatory and the anion inhibitory will be tested by using, as surrounding stimuli, a variety of organic and inorganic ions whose individual responses have first been measured. With chemical stimulation of the single papilla and electrical stimulation of surrounding papillae, summation of generator current from nerve branches will be examined as a mechanism of enhancement and depression. The purpose of this project is to investigate the roles of organic anions and cations in taste receptor excitation and inhibition, to determine the type of neurological interaction among multiple receptor inputs, and to quantify the integration of receptor input which occurs in the first nerve fiber. A better understanding of the ionic mechanisms of excitation in taste receptors would serve both scientific and technological application.